<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script type="text/javascript">

    var a=60;
    var b=0;
    if (a>=60){
        b=1;
    }else if (a>=70){
        b=2;
    }else if (a>=80){
        b=3;
    }else if (a>=90){
        b=4;
    }
    alert(b);
</script>

</body>
</html>